Viewer
From polycount
A viewer means You, the user of the game engine looking at the 3D scene through your computer screen.
The viewer looks into the game world from a vantage point, which acts something like a camera, to frame your view (Frustum). Most of the engine's calculations are tailored to make the world look great from that particular view.
Viewer may also refer to a version of the game engine that is used to preview artwork while it is being created.
